In recent years, instead of a liquid crystal display (LCD) having pixels containing liquid crystal elements, a display device having a light-emitting element typically such as an electroluminescence (EL) element has been studied and developed as a light-emitting device. The wide use of the light-emitting device has been expected as a display screen image or display device of a mobile telephone by taking advantage of high quality and wide viewing angles based on the light-emitting type and thinness and lightweight based on the unnecessity of backlights.
However, currently, from the viewpoint of the reliability (life) of an EL material, the luminance has been deteriorated, which is a problem. In a case where a multi-color display is conducted, there is a problem that the degrees of luminance deterioration differ among R, G and B elements.
Since the size and weight of a portable information terminal such as a notebook PC can be reduced significantly, the portable information terminal can be carried easily, and then can be more often used in an unstable state such as in a smaller place comparatively like in a train or an automobile and while walking. Since, in the use of the portable information terminal in such an unstable state, an operation of opening the lid of the notebook PC and manipulating keys by both hands are difficult, a portable information terminal has been demanded which can be used easily even on the move.